Hob and method of hobbing



Jan. 2, 1947. c. D. BARNARD ETI'AL 9 HOB AND METHOD 0? HOBBING Filed Aug. 2, 1940 2 Sheets-Sheet 1 INVENTOR HIIHHII Char/es Barnard l a 6 1 .9 a 4 5 .9 l0 l2 Mifihmz er C. Ha/yorsen BY v inoawava Jan. 23, 1947.

C. D. BARNARD ET AL HOB AND METHOD OF HOBBING Filed Aug. 2, 1940 2 Sheets-Sheet 2 INVENTOR [liar/ea D .Barnard Wander Ha/rorsefl w. @a v- W ATTORNEYS Mi 5v @119; M

Patented Jan. 28, 1947 HOB AND METHOD OF HOBBING Charles D. Barnard and-Mithander C. Halvorsen,

. Rockford, Ill.,

Company, nois assignors to Barber-Colman Rockford, 111., a corporation of Illi- Application August 2, 1940, Serial No. 349,614

The present invention relates to improvements in single position hobs and bobbing methods for cutting toothed elements, such as ratchets, etc. One of the objects is to provide a. novel single position hob having roughing and finishing teeth curves away from the roughing teeth so as to obviate the necessity for extensive, or any. mutilation for the purpose of avoiding tooth interference.

Other objects and advantages will become apparent as the description proceeds.

In the accompanying drawings,

Figure 1 is a perspective view of a hob embodying the features of our invention.

Fig. 2 is an enlarged fragmentary view illustrating' the relation of the hob and the work.

- Fig. 3 is a fragmentary end view of the hob.

Fig. 4 is a fragmentary plan view of the hob.

Figs. 5 to 5 are a series of fragmentary views illustrating successive teeth of the hob in their full depth cutting relation to one tooth of the work.

Fig. 6 is an enlarged fragmentary view gener ally similar to Fig. 2, but illustrating the relation of a conventional hob and the work.

Fig. 7 is an end view of the conventional hob.

While the invention is susceptible of various modifications and alternative constructions, we have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that we do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

'Referring more particularly to the drawings, the hob constituting the exemplary embodiment of our invention comprises a body I3 having a central bore I4 adapted to receive a suitable arbor I5. Formed on the periphery of the body I3 is a helical series of radially relieved hob teeth separated by gashes I6. These gashes may be either slightly inclined or straight relative to the 5 Claims. (Cl. 904) 2 bob axis. At least one convolution of hob teeth is provided, one convolution, comprising twelve successive teeth I to I2, being specifically shown. Each hob tooth has a front face I! defining a cutting edge [8, a top surface I9 and side surfaces and 2|, the top and side surfaces having a radial relief. Additional side clearance may be obtained when desired by inclining the teeth laterally to the hob helix, as indicated by the angle 0 (Fig. 4). The teeth I to I2 may be provided with any desired cutting contour depending upon thework to be hobbed. In the present instance, the hob is of the single position type adapted'to hob ratchets, and similar toothed elements, having raked or undercut teeth. One

form of ratchet is partially illustrated in Fig. 2,.

24, and which is to be formed with undercut peripheral teeth 25.

The leading hob teeth, for example, the teeth I to II, are roughing teeth adapted in their successive actions to take preliminary cuts progressively along the form of each tooth 25 of the work blank, and at least the last tooth I2 is a finishing tooth. All of the teeth I to I2 preferably have the same form or cutting contour.

Use of the hob entails a novel method of hobbing. In this method, the hob is positioned substantially transversely of the work axis, and is inclined slightly to a perpendicular to the axis to compensate for the hob helix angle. Also, the hob is located at one side of the center line of the work in such relation that the periphery of the work while passing through cutting engagement travels toward, instead of from, the hob axis. In the specific arrangement of Fig. 2, the ratchet 22 is rotatable counterclockwise about its axis 26, and the hob is rotatable clockwise as viewed from the right end about its axis 21. Consequently, the hob is located to the left of the center line 28 of the ratchet. If the work were rotatable in a clockwise direction, the hob would be reversed in form, and would be located to the right of the center line 23. With the hob and the work relativel located as shown in Fig. 2, both are rotated in such timed relation that .the hob will complete one revolution during rotation of the work through the distance of each tooth 25, i. e., through 36 where the ratchet has ten teeth. In this rotation, the hob teeth, from I to II, move successively through cutting engagement with each ratchetv tooth 25, and remove their proportionate share of metal DIOEIGS-y 5o sively along the form of the work. The roughing in conventional methods.

teeth I to II take preliminary cuts, and the lastor finishing tooth l2 takes a final cut as clearly illustrated in Figs. 5- to 5*, inclusive. It is to be understood that in the continued revolutions of the work blank, the hob is slowly fed relatively along the work axis 26.

It will-be noted that the portion of the periphery of the work blank 22 advancing toward the position of final engagement by the hob tooth I2 curves or drops away from the roughing teeth I to I I. As a result, little or no interference is encountered so that the hob may becylindrical in most instances, and, in special cases where mutilation may be desirable, the successive roughing teeth from II to I are stepped down or reduced in height only slightly, as indicated at A for the tooth I in Fig. 3.

By reason of the foregoing, the gashes II; are

- comparatively shallow and narrow, and the teeth I to I2 are correspondingl long in a peripheral direction and strong so that they may be frethereof. Consequently, along lifev is obtained,

and a rapid cutting feed is permitted.

The elimination or minimization of tooth inter- L ference permits of a material decrease in circular pitch of the hob so that many more teeth are brought into contact with the work, and the cutting load is unevenly distributed, the last or tooth 'I (Fig. 7), necessitates deep gashes I6, and a corresponding reduction in the peripheral length, stren th and life of the teeth. Also, the

of said element, rotating said element in a direction to advance that portion or the periphery I of said element which i in engagement with'said hob toward the axis orsaid hob,- and rotating said hob in timed relation to said element through one revolution for each rotation of said element through the distance of one element tooth.

2. The method of hobbing a rotary toothed element having peripheral teeth by a single poamount of stock removed by the teeth is substantially equalized. Heretoiore, the circular pitch of single position hobs has been approximately equal to that of the work. In the present instance, the circular pitch of the hob is considerably less than that of the work. Hence, the present hob and method result in a smooth cutting action.

.. The location of the hob is at the side of the center line of the work oppositeto that occupied Comparison is facilitated by reference to Figs. 6 and 7 which illustrate a conventional single position hob adapted to cut the same ratchet illustrated in Fig. 2. Like parts of the ratchet in Fig. 6are' therefore identified by the same reference numerals as in Fig. 2.

The conventional hob illustrated in Figs. 6 and 7 comprises a body Iiiormed with an axial bore I4, and with one convolution of twelve teeth I to I2 separated by flutes I6. Each of the teeth is spirally relieved, and has a cutting face II defining a contoured, cutting edge I8,

a top surface I9, and opposite side surfaces 20 and 21*.

tially to the secant line 29 (Fig. 6) extending across, the work blank inwardly oi the teeth 25. The extensive mutilation or step-down of the roughing teeth I to II,- as indicated at B for the sition hob having a helical convolution of relieved leading roughing teeth and a trailing finishing tooth of a smaller circular pitch than said element, said method comprising locating said hob in cutting relation .to said element with said finishing tooth disposed between said roughing teeth' and the center line of said element, and rotating said element and said hob in timed relation, with the periphery of said element at the point of cutting engagement moving toward-the hob axis. I

3. A method of hobbing a rotary toothed element having peripheral teeth comprising mounting a singleposition hob having a spiral convolution of teeth in cutting relation with said element wholly at one side of the centerline of said element, rotating said element and said hob in timed relation, taking a roughing out into the element by the leading teethof the hob, and taking a finish out along the entire contourcut in the element with a trailing tooth.

4. A single position cylindrical hob for formhobbing a rotary ratchet having undercut peripheral teeth, said hob comprising a rotary body hav-' ing only one helical convolution of relieved effective hob teeth of the same and uniform lead on opposite sides, said teeth having cutting contours all substantially the same and being of substantially equal height relative to the hob axis, the leading teeth being roughing teeth and the last trailing tooth being a finishing tooth.

5. A single position cylindrical hob'for formhobbing a rotary ratchet having undercut peripheral teeth, said hob comprising a rotary body having only one helical convolution of relieved effective hob teeth and adapted to be positioned en- I tirely at one side of the center line of the ratchet,

perpendicular to the hob axis in the path of the approaching ratchet teeth, the leading hob teeth being roughing teeth and the last trailing hob tooth being a finishing tooth having a cutting contour the same as the final complete contour 

